1. Field of the invention
This invention relates generally to a cross-polarization distortion canceller for use in a digital radio communication receiver, and more specifically to such a canceller provided in an intermediate frequency (IF) section of a digital radio communication receiver for re-establishing orthogonality of two orthogonally polarized transmitted signals.
2. Description of the Prior Art
The crowding of the frequency spectrum in a radio communication system has led to an extremely limited availability of transmission channels. A known approach to solving this problem is the use of the two orthogonally polarized waves for doubling the capacity of the radio communication system.
Under normal circumstances cross-polarization distortions, i.e. the effects of interference between such orthogonally polarized signals, are sufficiently low to result in overall good performance. However, when poor propagation conditions exist, such as during heavy rain, or air turbulence is present, or when the signals travel through a multipath communication medium, the cross-polarization distortions tend to increase and the two signals are not easily isolated merely on the basis of polarization.
In order to re-establish the orthogonality (i.e., to reduce or cancel the cross-polarization distortion), it has been proposed to provide an equalizer or compensating means in a digital radio communication receiver. A prior art equalizer or control means, however, has been installed in the baseband stage and hence requires a considerable number of transversal filters, resulting in a complex circuit configuration.